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Evaluation of Wildland Fire Chemicals
Standard Test Procedures (revised 5/15/06)

STP 9.1—Retention on a Dowel Tree


A measure of an enhanced water mixture consistency and retention on fuels can be obtained by the use of a simple dowel tree which is immersed and then removed from a test product and weighed.


  • Balance, readable to 0.001 grams
  • Test sample in quart jar or similar tall container
  • Dowel with hanger and support device

Dowel Tree Construction:Image of a wooden dowel with several smaller diameter dowels through the main dowel.

Prepare a simple dowel tree to evaluate the retention of water enhancer mixtures.

  • The trunk of the tree is a 0.5-inch dowel, six inches long.
  • A 0.125-inch hole drilled 0.25 inch from the top of the trunk serves as a hanger.
  • A thin, shallow line cut into the wood, two inches from the top of the trunk marks the immersion level.
  • Four holes to accommodate 0.125-inch dowels were drilled in the trunk starting 0.5 inch from the bottom of the trunk, at 0.5-inch intervals. Each hole is offset by 45 degrees from the hole below.
  • Dowels, 0.125-inch in diameter and 2.5-inches long were fitted snuggly into the holes and centered.

Test Method:

  1. Suspend a tree by a wire hanger or Dacron loop from a ring stand or similar support. Place the apparatus and tree on a balance capable of weighing to at least 1.0 mg. Ensure that the tree is suspended beyond the balance.
  2. Record the weight of the tree.
  3. Place a watch glass or other container below the tree, not on the balance.
  4. Using a lab jack or other support, place a quart jar of water enhancer mixture under the suspended tree.
  5. Adjust the lab jack to hold the water enhancer at a height to expose the tree to the immersion mark.
  6. Suspend the tree to the mark (bottom four inches on trunk) in a quart jar of water enhancer mixture for 60 seconds.
  7. Remove the tree from the mixture and record the weight of the suspended tree and apparatus every 10 seconds for a total of 60 seconds.
  8. Continue monitoring the weight at 60 second-intervals for 5 minutes.
  9. Prepare a graph of weight loss versus time.

Possible Scoring and Requirement:

Based on the amount of product remaining on the tree or the time to reach a selected percent of original quantity remaining, categorize each product as to retention.

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